1. Field of the Invention
The present invention generally relates to a beam-to-column joint to be utilized in the frame construction of buildings or other structures that are subject to seismic loads. In particular, the beam-to-column joint is a pin-fuse joint designed to lengthen dynamic periods and effectively reduce the forces that must be resisted within the frame so that the frame can withstand seismic activity without sustaining significant damage.
2. Description of the Related Art
Structures have been constructed, and are being constructed daily, in areas subject to extreme seismic activity. Special considerations must be given to the design of such structures. In additional to normal loading conditions, the frames of these structures must be designed not only to accommodate normal loading conditions, but also those loading conditions that are unique to seismic activity. For example, frame joints are typically subject to cyclic motions during seismic events. To withstand such loading conditions, structures subject to seismic activity must behave with ductility to allow for the dissipation of energy under these extreme loads.
In the past, most frame joints subject to seismic loads have been designed with the beam flanges connected directly to the column flanges via full penetration welds and with the beam webs either bolted or welded to columns. In recent seismic events, including the Northridge Earthquake in Northridge, Calif., moment-resisting frames of these types successfully prevented buildings from collapsing due to applied seismic loads. While these moment-resisting frames have proven successful in preventing buildings from collapsing, the frames have not done so without sustaining significant damage. After being subject to seismic loads, most of these types of moment-resisting frames have exhibited local failures of connections due to poor joint ductility. Such joint failures have raised significant concerns about the structural integrity and the economic performance of currently employed moment-resisting frames after being subject to an earthquake.
Since the Northridge Earthquake, extensive research of beam-to-column moment connections has been performed to improve the ductility of joints subject to seismic loading conditions. This research has lead to the development of several modified joint connections, one of which is the reduced beam section connection (“RBS”) or “Dogbone.” Another is a slotted web connection (“SSDA”) developed by Seismic Structural Design Associates, Inc. While these modified joints have been successful in increasing the ductility of the structure, these modified joints must still behave inelastically to withstand extreme seismic loading. It is this inelasticity, however, that causes joint failure and in many cases cause the joint to sustain significant damage. Although the amount of dissipated energy is increased by increasing the ductility, because the joints still perform inelastically, the currently designed joints still tend to become plastic or yield when subjected to extreme seismic loading.
Although current joint designs may be able to withstand a seismic event, the damage caused by the joints' inability to function elastically, raises serious questions about whether currently designed structures can remain in service after enduring seismic events. A need therefore exists for a moment resisting frame that can withstand a seismic event without experiencing significant joint failure so that the integrity of the structure remains relatively undisturbed even after being subject to seismic activity.